JPH04229087A - Ac motor driving method and power supply circuit for driving ac motor - Google Patents

Abstract

PURPOSE:To make it possible to reduce a load to a battery and operate for a longer period of time by giving an ordinary power in the initial stage of motor drive and then giving a smaller power than the initial power after the elapse of a certain period of time. CONSTITUTION:An output from a battery 2 is converted into AC by a switching element 9, rectified and smoothened by a rectifier 11 and smoothening circuit 13 and then supplied to and AC motor 23 through an inverter 18. Rotating speed of the AC motor is controlled by the inverter circuit 18. Width of pulses output from a pulse width-varying clock pulse generator 51 will be made wider for a certain period of time after the start of the AC motor 23 but made narrower thereafter. By doing this, the voltage supplied to the AC motor 23 becomes higher during start and lower at ordinary times, thereby reducing power consumption during steady-state operation.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an AC motor such as an induction (asynchronous) motor or a synchronous motor, and more particularly to a power supply circuit for driving an AC motor using a battery as a motor drive power source.

0002

2. Description of the Related Art FIG. 7 shows the configuration of a conventional induction motor drive power supply circuit using a battery, and FIG. 8 shows a timing chart showing its operation. Generally, the drive voltage of the AC motor is high voltage (e.g. 100 to 200 volts), while the output voltage of the battery 2 is low voltage (e.g. 12 volts).
It is. Therefore, in order to drive the induction motor 23, it is necessary to convert the battery voltage to a high voltage. For this purpose, the positive electrode of the battery 2 is connected to one end of the primary winding of a pulse transformer 12, and the channel of a power MOS transistor (FET) 10 is connected to the other end. A high frequency pulse signal output from the switching power supply IC3 is applied to the gate of the FET10, and the FET10
ET10 is made conductive intermittently. As a result, a high voltage pulse is generated across the secondary winding of the transformer 12. This high voltage pulse is rectified by a rectifier circuit made up of diodes 14 and 15, and then smoothed by a smoothing circuit made up of a choke coil 16 and a capacitor 17. In this way, a DC voltage E0 having a voltage value higher than the DC voltage of the battery 2 (for example, 141 volts) is obtained. Transistor 34, resistors 30 to 33, and Zener diode 35 constitute voltage comparator 38. The output of this voltage comparator 38 is applied to the switching power supply IC3 via the photocoupler 8 and the resistor 6 so as to maintain the DC voltage E0 at a constant voltage, and controls the pulse width of the output high-frequency pulse signal. The switching power supply IC3 is
For example, Hitachi HA16664APS.

[0003] The high DC voltage E0 is applied to the transistor 1
Switch circuit (inverter circuit) 18 consisting of 9 to 22
is converted into a pulsed alternating voltage V0. This pulsed alternating voltage V0 drives the induction motor 23 when the motor switch 24 is closed. The inverter circuit 18 is controlled by an astable multivibrator (AMV) 86 and a two-phase pulse generation circuit 56. Two-phase pulse generation circuit 5
6 is composed of a flip-flop (FF) 57 and AND gates 58 and 59. The pulse width and frequency of the pulse alternating voltage V0 are determined by the AMV86. Generally, this frequency is set to match the drive frequency standard for the motor 23, and the pulse width is set so that the effective value of the pulsed alternating voltage V0 matches the drive voltage standard for the motor 23.

0004

The amount of electricity that can be extracted from a battery is expressed as the product (Ah) of discharge current and discharge time. In order to extract electricity from the battery for a long time, it is necessary to use a battery with a large Ah.

[0005] However, batteries with a large Ah capacity are expensive, have large external dimensions, and are excessively heavy.

An object of the present invention is to provide a method for driving an AC motor that can be used for a longer period of time with a low-cost, small-sized battery, a power supply circuit for driving an AC motor, and an uninterruptible power supply for driving an AC motor using the same. It's about doing.

[0007]

[Means for Solving the Problems] A method for driving an AC motor according to the present invention converts a DC battery voltage into a DC high voltage, and then converts the DC high voltage into a pulsed alternating voltage having a first pulse width. In an AC motor driving method for driving a motor, when a predetermined period has elapsed after the start of driving the AC motor, the pulse width of the pulsed alternating voltage is changed to the first
The second pulse width is changed to a second pulse width narrower than the pulse width of the second pulse width.

Another method for driving an AC motor according to the present invention is to convert a DC battery voltage into a DC high voltage having a first voltage value, and then convert the DC high voltage into a pulsed AC voltage to drive an AC motor. In the AC motor driving method, when a predetermined period of time has elapsed after the start of driving the AC motor, the voltage value of the DC high voltage is lowered to a second voltage value lower than the first voltage value.
The voltage value is changed to .

[0009]

[Operation] Since the motor rotates at a high speed (approximately 1,500 revolutions per minute), it is often decelerated by a speed reduction mechanism such as a gear or a belt to utilize its power. In such a case, a large force is required at the initial stage of motor drive due to inertia and static friction. However, once rotation begins, a relatively small force is often sufficient.

[0010] The inventor of the present invention focused on this point, and applied normal electric power at the initial stage of motor drive, and after a certain period of time, applied electric power smaller than the initial electric power. for that,
Controls the pulse width or pulse voltage value (peak value) of the pulsed alternating voltage that drives the AC motor. This reduces the load on the battery and enables long-term operation. Furthermore, the battery can be made smaller and lighter.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described in detail, taking a power supply circuit for driving an induction motor as an example.

First, FIG. 1 shows the configuration of an embodiment of an AC motor driving power supply circuit according to the present invention. In addition, in each figure of this specification, the same reference number is attached to the same element. One end of the battery 2 is connected to one end of a primary winding of a transformer 12, and a switching element 9 is connected between the other end of the primary winding and ground. The switching element 9 is
It is periodically turned on and off by a high frequency pulse signal output from the switching control circuit 4. A rectifier 11 is connected to both ends of the secondary winding of the transformer 12, and the output of the rectifier 11 is smoothed by a smoothing circuit 13. Smoothing circuit 1
The output DC voltage E0 of No. 3 is compared with a reference voltage Vr1 by a comparator 38. The output of the comparator 38 is fed back to the switching control circuit 4, and the pulse width of the high frequency pulse signal of the switching control circuit 4 is controlled so that the output voltage E0 matches Vr1. The output voltage E0 is converted into a pulsed alternating voltage V0 by the inverter circuit 18. This pulse alternating voltage V0 is applied to the induction motor 23 via the motor switch 24.
is applied to. The switch 24 is a switch for driving the motor 23, and when it is closed, the motor 23 is turned on. As the switch 24, in addition to a manual switch, a magnetically controlled relay, an electrically controlled transistor, etc. can be used. The inverter circuit 18 is controlled by a two-phase pulse signal from a two-phase pulse generation circuit 56. In order to control the drive of the motor, a switch (see 93 in FIG. 6, which will be described later) that connects and disconnects the power supply from the battery 2 to the transformer 12 may be provided instead of using the motor switch 24.

The above configuration is substantially the same as the conventional power supply circuit shown in FIG. The difference from the power supply circuit of FIG. 7 lies in the following configuration. The means for detecting that the motor 23 is driven includes a resistor 36 connected between the inverter circuit 18 and the ground, and a detector 54 that detects when the voltage across the resistor 36 exceeds a predetermined value. provided. Furthermore, a delay circuit 55 that delays the output of the detector 54 by a predetermined time and outputs the delayed output, and a variable pulse width clock generator 51 whose pulse width is controlled by the output of the delay circuit 55 are provided. The output clock of this variable pulse width clock generator 51 is input to a two-phase pulse generation circuit 56.

FIG. 2 shows the detailed configuration of each part in FIG. 1 in more detail. Switching control circuit 4, switching element 9, rectifier circuit 11, smoothing circuit 13, inverter circuit 1
8. The voltage comparator 38 can be constructed from the same components as the conventional power supply circuit shown in FIG.

The detection circuit 54 includes a transistor 37, a capacitor 39, and resistors 40 and 41. This detection circuit 54 includes a resistor 3 that detects the current flowing through the motor 23.
It is detected that the voltage across the transistor 6 has exceeded a predetermined value (the transistor 37 is turned on), and a low level signal is output to the collector of the transistor 37. The capacitor 39 is provided to prevent the collector of the transistor 37 from returning to a high level during a minute off period of the pulsed alternating voltage while the motor 23 is being driven.

The delay circuit 55 includes a monostable multivibrator (MMV) 49, resistors 47 and 48, a capacitor 44,
46, and a variable resistor 45. MMV49 is, for example, a commercially available retriggerable one-shot IC, HD
1438BP can be used. The output of the detection circuit 54 is applied to the input terminal of the MMV 49 via the capacitor 44, and is also applied to the input terminal of the MMV 49 by the resistors 48 and 47.
It is added and synthesized with the output of MV49. A variable resistor 45 and a capacitor 46 are used to determine the output pulse width of the MMV 49. By adjusting the variable resistor 45, the output pulse width can be changed. The capacitor 46 instead of the resistor 45 may be used as a variable element. The resistor 47 and the resistor 48 can also be replaced with an OR gate that ORs the output of the detection circuit 54 and the output of the MMV 49.

The variable pulse width clock generator 51 includes an astable multivibrator (AMV) 52 that generates clock pulses of a constant period, and an MMV 53 that is driven by the output pulses. The MMV 53 outputs a pulse with a predetermined pulse width every time it receives a pulse at its input terminal. This predetermined pulse width is determined according to the output from the delay circuit 55. For both the AMV52 and MMV53, for example, a commercially available timer IC, NE555, can be used. Here, two elements are used as the variable pulse width clock generator 51, but if there is a single element that can externally control the pulse width of a constant period pulse output, it may be used. Working voltage 100V, 50H
In the case of a motor of
The pulse width is set to a value such that the effective value of the pulsed alternating motor voltage V0 becomes 100V.

As means for detecting the drive of the motor 23, a resistor 36 and a detector 54 are provided, but the switch 24
The detection signal (in the embodiment, a high level signal) may be generated using the detection signal itself or a switch (not shown) in conjunction with the detection signal. Alternatively, it is also possible to use the control signal of the switch 24 as the detection signal.

Next, the operation of each part in FIG. 2 will be explained with reference to the timing diagram in FIG. While the motor switch 24 is off, the voltage across the resistor 36 that detects the current flowing through the motor 23 is insufficient to turn on the transistor 37. Therefore, the output of the detection circuit 54 is held at a high level via the resistor 41. During this time, the delay circuit 55
The output of the MMV 49 in the circuit is at a low level, but since the output of the detection circuit 54 is at a high level, the output of the detection circuit 54 is also at a high level. The AMV 52 in the variable pulse width clock generator 51 generates a clock pulse with a constant period, and in response, the MMV 53 generates a pulse with a pulse width determined according to the output of the delay circuit 55. This MMV
The output pulse 53 is output from FF5 in the two-phase pulse generation circuit 56.
The frequency is divided by 1/2 by 7. The two-phase pulses that are the frequency-divided outputs are processed by AND gates 58 and 59, respectively.
It is ANDed with the output pulse of MMV53. As a result, a two-phase pulse signal having the same pulse width as the output pulse of the MMV 53 is obtained at the output of both AND gates.

Note that if there is a switch for the entire power supply circuit on the battery 2 side, there is no problem even if the operation starts from time t3 in FIG.

When the motor is turned on at time t1, the transistor 37 in the detector 54 is turned on and its output becomes low level. This low level signal causes the MMV49
is triggered and its output changes to high level. This high level output continues for a time T determined by the time constants of variable resistor 45 and capacitor 46. MMV49
Because of the high level output of , even though the output of the detector 54 has changed to low level, the output of the delay circuit 55 remains at high level. Therefore, the output pulse width TX of the MMV 53 controlled by the output voltage of the delay circuit 55 does not change. When the output of the MMV 49 returns to low level at time t2 after time T, the output of the delay circuit 55 (i.e.,
The control voltage of MMV53) becomes low level for the first time, and as a result, the output pulse width of MMV53, that is, the pulse width of pulsed alternating motor voltage V0, changes from TX to TY, which is narrower than this.
Changes to The period T0 itself of the pulsed alternating motor voltage V0 does not change. The pulse width TY is set to a value that allows steady operation to be maintained after the motor is started. Maintaining steady operation is
There are considerable differences depending on the type of motor load, so it is best to set it based on actual measurements. When the motor is turned off at time t3, the output of the detector 54 returns to high level. In response to this,
The output of delay circuit 55 immediately returns to high level. As a result, the pulse width of MMV53 also returns to the original TY. In this embodiment, the delay circuit 55 does not have the function of delaying the output of the detector 54 when the motor is turned off, but there is no problem. This is because the specifications shown in FIG. 3 only need to be guaranteed when the motor switch is on and during the on period.

According to this embodiment, the pulse width of the motor voltage V0 is equal to the pulse width T for several seconds (time T) when the motor is started.
Y, but the pulse width is TX during the subsequent steady operation period. Therefore, if TY is set to 70% of TX, for example,
During steady operation, battery power consumption can be reduced by 30%. As a result, the weight and size of the battery can also be reduced.

FIG. 4(a) shows another example of the structure of the delay circuit 55 together with related parts. This delay circuit 55 includes operational amplifiers 76 and 78, resistors 71 and 74, a diode 72, and a capacitor 73. The diode 72 is for discharging the charge in the capacitor 73 after the motor switch 24 is turned on. The resistor 74 is for setting the output to 0 volts when the input is 0 volts. It is assumed that the resistance value of the resistor 74 is sufficiently larger than the resistance value of the resistor 71.

As shown in the timing diagram of FIG. 4(b),
When the motor 23 is turned on, the potential of the node A drops to near the negative potential of the capacitor 17, and the difference signal from +Vr3 is integrated by the operational amplifier 76. That is, the potential of the output node B of the operational amplifier 76 is determined by the time constant R71·C7.
It rises at 3. When this rising waveform reaches the reference voltage +Vr2, the output of the operational amplifier 78 is inverted, and the voltage at the node C becomes low level. As can be seen from the figure, the change in voltage at node A after the motor is turned on appears as a change in voltage at node C with a delay. If a variable element is used for the resistor 71 (or capacitor 73), the delay time can be made variable.

In the embodiment described above, the pulse alternating voltage V
0 pulse width was adopted, but next, the voltage value (pulse peak value) of the pulse alternating voltage V0 was adopted.
Another embodiment that employs a method of controlling will be described.

FIG. 5(a) shows the configuration of the main part of another embodiment of the present invention. In this embodiment, the voltage comparator 38 in the first embodiment is replaced with another voltage comparator 90, and the variable pulse width clock generator 51 is replaced with an AMV (FIG. 7) similar to the conventional one. The voltage comparator 90 has a configuration of the voltage comparator 35 with a new transistor 82 and resistors 81 and 83 added. transistor 8
2, the output of the delay circuit 55 described above is connected to the resistor 8.
3. As shown in FIG. 5(b), after a predetermined period of time has passed after the motor is turned on, the output of the delay circuit 55 changes from high level to low level. When at high level, transistor 82 is on. At this time, the resistor 81 is connected in parallel to the resistor 33. The DC voltage E0 is maintained such that the value obtained by multiplying the voltage division ratio by the parallel combined resistance and the resistor 32 by the DC voltage E0 is equal to the voltage value VZ of the Zener diode 35. The voltage E0 (H) at this time is the parallel combined resistance value R
, if the resistance value of the resistor 32 is R32, then E0(H)={
(R32+R)/R}VZ. When the output of the delay circuit 55 becomes low level, the transistor 82 is turned off. Therefore, the voltage division ratio of the DC voltage E0 is determined only by the resistors 32 and 33. The voltage E0 at this time is the resistance 3
If the resistance value of 3 is R33, E0(L)={(R32+R33)/R33}VZ. Since the resistance value R is smaller than the resistance value R33, E(
H)>E(L). Therefore, the pulsed alternating voltage E
The pulse height value of 0 is also determined accordingly. That is, the battery power can be saved in proportion to the voltage E0 reduction rate.

Next, FIG. 6 shows a schematic configuration of an uninterruptible power supply device for an AC motor using the AC motor drive power supply circuit of the present invention. This uninterruptible power supply device includes the power supply circuit 9 described above.
6 (Battery 2 and motor 23 in the circuit shown in Figure 1 etc.)
), a charging control circuit 91 that charges the battery 2 by receiving the commercial power supply voltage, and a switch circuit 93
and 94, power outage detection and switch circuits 93, 94
It consists of a power failure detection/switch control circuit 92, a motor drive switch 95, and a motor 23. The switch circuits 93 and 94 can be composed of relays, photocouplers, transformers, and the like. In addition, in the figure, the commercial power supply line and the motor drive line are shown as one line for simplification.

In this uninterruptible power supply, the switch circuit 93 is normally turned off, and the switch circuit 94 is switched to the commercial power supply side. To drive the motor, simply close the motor drive switch 95, either manually or automatically. When a power outage occurs, the power outage detection/switch control circuit 92 detects the power outage, switches the switch circuit 94 to the power supply circuit 96 side, and turns on the switch circuit 93. As a result, the power supply circuit 96 starts operating, and the motor 23 is driven by the power of the battery 2.

This uninterruptible power supply is suitable for use in emergency applications that require motor drive even during power outages, such as fire shutters, automatic doors, garage shutters, etc.

[0030] In the above embodiment, only an induction motor was explained, but the invention can also be applied to a synchronous motor. Further, the present invention can also be applied to polyphase motors. In the case of multi-phase, the pulse alternating voltage may be prepared for the number of phases, and pulse width control or voltage value control may be performed for each phase. Furthermore, in the above embodiment, pulse width control, etc. is performed after a certain period of time has passed after the motor starts driving. It is also possible to return to the same state as at the initial stage of driving (that is, to take measures to reduce power consumption only during the steady state period).

[0031]

According to the present invention, the power consumption of a battery for driving an AC motor can be reduced, so that the life of the battery can be extended. Conversely, if the lifespan is the same as before, the battery can be made smaller and lighter. Therefore, the cost of the battery can also be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing a schematic configuration of an embodiment of an AC motor drive power supply circuit according to the present invention.

FIG. 2 is a circuit diagram showing a detailed configuration of the embodiment of FIG. 1;

FIG. 3 is a timing diagram showing the operation of the embodiment of FIG. 2;

4 is a circuit diagram showing a modification of the delay circuit 55 in the embodiment of FIG. 1, and a timing chart showing its operation.

FIG. 5 is a circuit diagram showing a main part of the configuration of another embodiment of the present invention and a timing diagram showing its operation.

FIG. 6 is a block diagram showing the configuration of an uninterruptible power supply device for driving an AC motor according to the present invention.

FIG. 7 is a circuit block diagram showing the configuration of a conventional AC motor drive power supply circuit.

8 is a timing diagram showing the operation of the power supply circuit of FIG. 7. FIG.

[Explanation of symbols]

2... Battery, 4... Switching control circuit, 9... Switching element, 12... Pulse transformer, 11... Rectifier circuit,
12... Smoothing circuit, 18... Switch circuit (inverter circuit), 23... Induction motor, 24... Motor switch, 36...
Resistor, 38... Voltage comparator, 51... Pulse width variable clock generator, 54... Detection circuit, 55... Delay circuit, 56... Two-phase pulse generation circuit, 91... Charging control circuit, 92... Power failure detection/switch control circuit, 93, 94...Switch circuit, 95
...Motor drive switch, 96...Power supply circuit.

Claims (7)

[Claims] 1. An AC motor driving method comprising converting a DC battery voltage into a DC high voltage and then converting the DC high voltage into a pulsed alternating voltage having a first pulse width to drive an AC motor. An AC motor driving method, characterized in that, after a predetermined period has elapsed after the start, the pulse width of the pulsed alternating voltage is changed to a second pulse width narrower than the first pulse width. 2. In an AC motor driving method, the AC motor is driven by converting a DC battery voltage into a DC high voltage having a first voltage value, and then converting the DC high voltage into a pulsed alternating voltage to drive the AC motor. An AC motor driving method characterized in that, after a predetermined period of time has elapsed after starting, the voltage value of the DC high voltage is changed to a second voltage value lower than the first voltage value. 3. An AC motor drive method in which a DC battery voltage is converted to a DC high voltage, and then the DC high voltage is converted to a pulsed alternating voltage to drive an AC motor, wherein after the AC motor starts driving, the AC motor is brought into a steady state. An AC motor driving method characterized in that during a certain period, at least one of a first control that narrows the pulse width of the pulse alternating voltage and a second control that reduces the pulse peak value is performed. 4. A power supply circuit for driving an AC motor using battery voltage, comprising: voltage conversion means for converting the DC voltage of the battery into a DC high voltage; and a voltage conversion means for converting the high voltage obtained by the voltage conversion means. an alternating voltage generating means for converting into a pulsed alternating voltage having a first pulse width; a detecting means for detecting voltage application to the motor; and when the starting of the motor is detected by the detecting means, after a predetermined period has elapsed; A power supply circuit for driving an AC motor, comprising pulse width changing means for changing the pulse width of the pulsed alternating voltage to a second pulse width narrower than the first pulse width. 5. The pulse width changing means includes a delay circuit receiving the output of the detecting means, a clock generator whose pulse width is controlled by the output of the delay circuit, and an output clock of the clock generator that changes the output clock of the clock. Claim 4 characterized by comprising: a two-phase pulse generator that converts into a two-phase pulse signal having a pulse width; and a switch circuit that converts the DC high voltage into a pulsed alternating voltage according to the two-phase pulse. The described AC motor drive power supply circuit. 6. An AC motor drive power supply circuit for driving an AC motor using battery voltage, comprising voltage converting means for converting the DC voltage of the battery into a DC high voltage having a first voltage value;
an alternating voltage generating means for converting the high voltage obtained by the voltage converting means into a pulsed alternating voltage; a detecting means for detecting voltage application to the motor; and voltage value changing means for changing the voltage value of the DC high voltage to a second voltage value lower than the first voltage value after a period of time has elapsed. 7. A battery, a power supply circuit for driving an AC motor according to claim 4, 5 or 6, which is driven by the battery, power failure detection means for detecting a power failure of the commercial power source, and supplying power to the AC motor. An uninterruptible power supply device for driving an AC motor, comprising a switching means for switching between a commercial power supply and the AC motor drive power supply circuit as a power source.